package org.eclipse.moquette.parser.netty;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.handler.codec.CorruptedFrameException;
import io.netty.util.Attribute;
import io.netty.util.AttributeMap;
import org.eclipse.moquette.proto.messages.AbstractMessage;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.UnsupportedEncodingException;

/**
 * Created by alex on 15-5-19.
 */
public class Utils {

    public static final Logger LOG = LoggerFactory.getLogger(Utils.class);

    public static final int MAX_LENGTH_LIMIT = 268435455;

    public static final byte VERSION_3_1 = 3;
    public static final byte VERSION_3_1_1 = 4;

    /**
     * 读取MessageType
     * MessageType 存储在第一个字节的后4位
     * --------------------------------------------------------|
     * | bit  | 7  | 6  | 5  | 4  | 3       | 2  | 1  | 0      |
     * |-------------------------------------------------------|
     * |1byte |   MessageType     |DUP flag |Qos level| RETAIN |
     * |-------------------------------------------------------|
     * |2byte |         Remaining Length                       |
     * |-------------------------------------------------------|
     * @param in
     * @return
     */
    static byte readMessageType(ByteBuf in){
        byte h1 = in.readByte(); //得到第一个字节的
        byte messageType = (byte) ((h1 & 0x00F0) >> 4); //得到代表messageType的4位的值
        return messageType;
    }

    /**
     * 把string 编码到ByteBuf中, 第一个字节存储string的长度，后续的字节存储string的内容
     * Return the IoBuffer with string encoded as MSB, LSB and UTF-8 encoded
     * @param str
     * @return
     */
    public static ByteBuf encodeString(String str){
        ByteBuf out = Unpooled.buffer(2);
        byte[] raw;
        try {
            raw = str.getBytes("UTF-8");
            //NB every Java platform has got UTF-8 encoding by default, so this
            //exception are never raised.
        }catch (UnsupportedEncodingException ex){
            LOG.error(null,ex);
            return null;
        }

        out.writeShort(raw.length); //写入字符串的 字节长度
        out.writeBytes(raw);        //写入字符串字节
        return out;
    }

    /**
     * 除了messageType 得到剩余部分的的长度ByteBuf
     * @param value
     * @return
     * @throws CorruptedFrameException
     */
    static ByteBuf encodeRemainingLength(int value) throws CorruptedFrameException {

        //保证值有意义
        if (value > MAX_LENGTH_LIMIT || value < 0) {
            throw new CorruptedFrameException("value should in range 0.." + MAX_LENGTH_LIMIT + " found " + value);
        }

        ByteBuf encoded = Unpooled.buffer(4);
        byte digit;
        do {
            digit = (byte) (value % 128);
            value = value / 128;
            // if there are more digits to encode, set the top bit of this digit
            if (value > 0) {
                digit = (byte) (digit | 0x80);
            }
            encoded.writeByte(digit);
        } while (value > 0);
        return encoded;
    }

    /**
     * 解码剩余部分的的长度
     * Decode the variable remaining length as defined in MQTT v3.1 specification
     * (section 2.1).
     *
     * @return the decoded length or -1 if needed more data to decode the length field.
     */
    static int decodeRemainingLength(ByteBuf in){
        int multiplier = 1;
        int value = 0;
        byte digit;

        do {
            if (in.readableBytes() < 1) {
                return -1;
            }
            digit = in.readByte();
            value += (digit & 0x7F) * multiplier;
            multiplier *= 128;
        } while ((digit & 0x80) != 0);
        return value;
    }

    /**
     * 检查头是否可用
     * @param in
     * @return
     */
    static boolean checkHeaderAvailability(ByteBuf in) {

        if (in.readableBytes() < 1) {
            return false;
        }

        in.skipBytes(1);

        //检查可变部分的长度
        int remainingLength = Utils.decodeRemainingLength(in);
        if (remainingLength == -1){
            return false;
        }

        if (in.readableBytes() < remainingLength ){
            return false;
        }

        return true;
    }

    /**
     * Load a string from the given buffer, reading first the two bytes of len
     * and then the UTF-8 bytes of the string.
     *
     * @return the decoded string or null if NEED_DATA
     */
    static String decodeString(ByteBuf in) throws UnsupportedEncodingException {
        if (in.readableBytes() < 2){
            return null;
        }

        int strLen = in.readUnsignedShort();
        if (in.readableBytes() < strLen){
            return null;
        }
        byte[] strRaw = new byte[strLen];
        in.readBytes(strRaw);

        return new String(strRaw, "UTF-8");
    }

    /**
     * 编码byte1 Flags
     * @param message
     * @return
     */
    static byte encodeFlags(AbstractMessage message){
        byte flags = 0;

        if (message.isDupFlag()){
            flags |= 0x08;
        }

        if (message.isRetainFlag()){
            flags |= 0x01;
        }

        flags |= ((message.getQos().ordinal() & 0x03) << 1);
        return flags;
    }

    static boolean isMQTT3_1_1(AttributeMap attrsMap) {
        Attribute<Integer> versionAttr = attrsMap.attr(MQTTDecoder.PROTOCOL_VERSION);
        Integer protocolVersion = versionAttr.get();
        if (protocolVersion == null){
            return true;
        }
        return protocolVersion == VERSION_3_1_1;
    }

    static int numBytesToEncode(int len) {

        if (0 <= len && len <= 127) return 1;
        if (128 <= len && len <= 16383) return 2;
        if (16384 <= len && len <= 2097151) return 3;
        if (2097152 <= len && len <= 268435455) return 4;

        throw new IllegalArgumentException("value shoul be in the range [0..268435455]");
    }

}
